1. Field
Aspects of the present invention relate to method and apparatus for tracking a maximum power point and method of operating a grid-tied power storage system using the same.
2. Description of Related Art
Recently, the European Union has decided upon a plan to expand the percentage on the use of renewable energy sources, from among all electric power sources, to be up to 20% in the year 2020 and 50% in the year 2050. The United States is also planning to carry out Renewable Portfolio Standards (RPSs). In a situation where, among all the electric power sources, renewable energy use increases from less than 5% at today's level to 30 to 40% in the future, a power system should be prepared for the upcoming changes.
It is not easy to control the amount of generation of renewable energy. This is because the amount of generation of renewable energy fluctuates according to environmental conditions, such as solar power (e.g., solar lighting), wind power, and wave power. Research is being done on a scheme capable of overcoming degradation in the power quality of a power system and a mismatch between production and consumption times, which may occur because of the changing availability of renewable energy. Power quality is evaluated on the basis of voltage and frequency. If the supplied quantity of renewable energy does not coincide with the demanded quantity of renewable energy in real time, abnormalities are generated in voltage and frequency, thereby being capable of deteriorating the power quality of all power systems.
A power storage system has been considered as an alternative solution capable of managing the changing availability of renewable energy. This is because the power storage system can efficiently control demand and supply by storing electric energy when the amount of generation of renewable energy exceeds demand and discharging electric energy when the demand exceeds the amount of generation of renewable energy.
Power storage techniques include pumping-up power generation, Compressed Air Energy Storage (CAES), flywheel, Superconducting Magnetic Energy Storage (SMES), rechargeable battery, etc. The pumping-up power generation technique is a method of generating electricity by rotating a turbine by scooping up water in a dam when surplus electricity is available and discharging water from the dam when electricity is insufficient. The CAES technique is a method of generating electricity by compressing air in the ground or sea and then discharging the air as occasion demand to generate electricity. The flywheel technique is a method of generating electricity by rotating a top when electricity is left over and rotating a power generator using the top when electricity is insufficient. The SMES technique is a method using a principle that current can be stored in a superconducting coil having substantially zero resistance. The rechargeable battery technique is method of utilizing a battery that can be repeatedly charged and discharged and has been used in an Uninterruptible Power Supply (UPS) for temporarily supplying electricity upon a power failure. The rechargeable battery has recently been held in the spotlight as an auxiliary power of renewable energy system.
In solar power generation, power can be generated by installing solar cell modules on a house, a building, etc. However, Maximum Power Point Tracking (MPPT) control for extracting a maximum power has to be performed because the solar power generation has low power generation efficiency. In solar power generation, the efficiency of power generation can be determined according to how quickly a maximum power point is found and how stably the maximum power point is maintained on the basis of the MPPT control.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.